Science ( Making use of Electricity (8.6 only) )

Question 1

All electrical appliances are _____ _____. They convert electrical energy to other _____ of energy

Answer 1

• energy converters
• forms

Question 2

A hair dryer converts _______ energy to the ______ energy of the fan, the thermal energy given out by the heating coil and the ____ energy given out by different parts of the hair dryer.

Answer 2

• electrical
• kinetic
• sound

Question 3

True or false
1 Mains electricity is generated in power stations.
2 The mains voltage in Hong Kong is 220 V.
3 The sockets in a home are connected in series.
4 Electricity is supplied to our homes through the live wire and the earth wire.

Answer 3

1T
2T
3F
4F

Question 4

Which of the following electrical appliences use the heating effect of current?
(1) Toaster
(2) Electric iron
(3) Electric kettle

Answer 4

1 2 and 3

Question 5

Which of the following electrical appliences use the magnetic effect of current?
(1) Electric fan
(2) Rice cooker
(3) Vacuum cleaner

Answer 5

1 and 3

Question 6

What is the color of live wire, Neutral wire and Earth wire

Answer 6

Live wire: brown
Neutral wire: Blue
Earth wire: Green and Yellow

Question 7

Which wire is connected to the fuse?

Answer 7

Live wire

Question 8

1 When too many electrical appliances are connected to a mains socket, _________ occurs
2 A ______ breaks a circuit when the current becomes too large. It has a metal wire with a low melting point. The number on it is the _______.

Answer 8

overloading
fuse
fuse rating

Question 9

A ________ _ also cuts off the current when the current becomes too large. We can reset it from the ‘OFF’ mode to the ‘ON’ mode.

Answer 9

Circuit breaker

Question 10

T or F
1 overloading and short circuits are dangerous and should be avoided.
2 Fuses and circuit breakers reduce the risk of the circuit overheating
3 A suitable fuse should have a rating much higher than the normal operating current of the applience.
4 A fuse can be reset after it blows
5 The live, neutral and earth wires of an appliance all carry a current under normal operations.

Answer 10

1 T
2 T
3 F
4 F
5 F

Question 11

The fuse rating is usually marked in _______.

Answer 11

ampere

Question 12

The fuse in a three-pin plug should be connected to ________.

Answer 12

the live wire

Question 13

A vacuum cleaner normally works with a current of 9A. If a 5A fuse is used, what happens?

Answer 13

The fuse blows and the cleaner cannot operate

Question 14

What is the use of the earth wire in a three-pin plug?

Answer 14

To protect the user from getting an electric shock.

Question 15

Which of the following statements about earth wire are correct?
(1) The earth wire connects the metal case of the appliance to the ground.
(2) The current flows to the ground through the earth wire when the live wire touches the metal case accidentally
(3) The earth wire blows when a fault occurs.

Answer 15

1 and` 2

Question 16

When an electric fans is full of dust, what possible danger is there? (state one) And how can we prevent this?

Answer 16

Short circuit
Clean the fan

Question 17

When a short circuit occurs, a large ______ flows in the circuit. This may ______ and damage the fan.

Answer 17

Current
overheat

Question 18

What happens if there too many electrical appliances connected to a single mains socket?

Answer 18

• Too many electircal appliances are connected to a single mains socket
  -> Current flowing through the circuit may become very large
  -> Overloading may occur
  -> Strong heatin effect of the large current may result in a fire

Question 19

What happens during a short circuit?

Answer 19

• Short circuit
  -> WIre provides a path with very low resistance
  -> A large current will pass through the wire
  -> Large current causes the thin wire to heat up and glow.
  -> May overheat and damage an electrical appliance

Question 20

What is the working principle of the fuse?

Answer 20

*Principle of fuse
-> Current passing through the fuse is larger than the fuse rating
-> Meral wire in the fuse melts and the fuse blows
-> The circuit becomes open
-> Current is cut off to prevent the circuit from overheating

Question 21

State the function of the earth wire.

Answer 21

• Function of the earth wire
  -> If the live wire is damaged and it touches the metal case of an electrical appliance.
  -> The circuit is shorted by the earth wire. Current flows to the ground through the
  earth wire and blows the fuse.
  -> The current from the mains is cut off. This protects us from an electric shock.